1. Field of the Invention
The present invention relates to an automatic exposure control system for a single lens reflex camera and more particularly relates to an exposure control system of the type wherein light from an object to be photographed (an object light) is measured by a light measuring device through a camera objective and a diaphragm aperture which is being varied due to driving of the diaphragm blades from a full open position to an advanced stopped-down position, or vice versa, until the blades are stopped when the output of the light measuring device reaches a given level with respect to a set shutter speed and a film sensitivity, whereby a suitable diaphragm aperture is set or determined automatically.
2. Description of the Prior Art
Exposure control systems of the above mentioned type have been proposed. In the known systems, however, the reflex mirror is actuated to move from its viewing position to its photographic position, by a member of the diaphragm driving mechanism when the member approaches its terminal position after its further travel subsequent to the determination of the diaphragm aperture, or by a mechanical member responsive to the diaphragm blade stopping operation.
In the former case, i.e. mirror actuation by a member of a diaphragm drive mechanism, some delay always occurs between the determination of a diaphragm aperture and the actuation of the mirror, while in the latter case, i.e. the actuation of the mirror by a mechanical responsive member, the mechanical linkage between the diaphragm stopping member and the mirror actuating member is complex and causes some mechanical delay during the transmission of the movement, because the stroke of the diaphragm stopping member, which may have the form of, for example, a lever with an armature controlled by an electromagnet, must be small to ensure exactness of the diaphragm aperture determination and such a movement of the small stroke must be transmitted. This will be easily understood from the consideration that if the stroke is large then the diaphragm blades move a little further during the travel of the stopping member after the actuation of the electromagnet. In other words, the stopping member must have a short stroke to stop the diaphragm blades immediately after a stop signal is generated to actuate the electromagnet.